Izaguirre suffered the injury in the 2-2 draw with Dundee United on Sunday, a game that also cost Celtic the services of centre-back Thomas Rogne, who hurt his calf.
They join a long list of injured players who will miss Wednesday's Champions League date with Barcelona at Celtic Park, with midfielder James Forrest (hamstring) and forward Lassad (groin) also ruled out.
Gary Hooper is a doubt but Lennon hopes to have Nou Camp scorer Giorgios Samaras and midfielder Scott Brown back among his options.
Lennon said: "It's hugely disruptive as they are big players, have been for a while and were pivotal to how we wanted to play on Wednesday, but we still have a strong team to play.
"It is important he (Samaras) makes it anyway. He has been unlucky this season with injuries. Obviously he came back from Barca & played very well until he picked up the ankle injury. We are hoping he is going to make kick-off.
"It will be a great occasion for the club. It's our anniversary and something we are very proud of. It's a pivotal year for us, a year of celebration, and this would be the crowning glory in that year.
"You have to play at your very best, with full concentration and great intensity.
Sometimes even then that's not enough but we'll have a full house.
"We played very well in Barcelona, and at home and the crowd will inspire the players. Tomorrow night is important. If we can get something out of the game it would give us a strong foothold in the group."